Receptors for Epidermal Growth Factor in the Rat Uterus*

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Abstract
Uterine membranes contain high affinity [(Kd) = 0.36 nM], saturable binding sites for [125I]iodo-epidermal growth factor (EGF). The binding of [125I] iodo-EGF is specific since it is abolished by excess unlabeled EGF but not by excess unlabeled insulin, fibroblast growth factor or multiplication-stimulating activity. Incubation of [125I] iodo-EGF with uterine membranes, followed by chemical crosslinking with disuccinimidyl suberate and detergent extraction reveals a major species of specifically bound EGF (MW = 170,000) and a minor species (MW = 150,000) visualized by autoradiography of sodium dodecyl sulfate gels after electrophoresis of the extracts. In detergent-solubilized preparations EGF also stimulates the phosphorylation of major (MW = 170,000) and minor (MW = 150,000) species of identical MW. The increased phosphorylation produced by incubation of membrane extracts with EGF occurs largely at tyrosine residues, as indicated by phosphoamino acid analysis. Apparently, the rat uterus contains high affinity EGF binding sites with the properties expected of EGF receptors.